Process for preparing phthalides

ABSTRACT

A process for preparing phthalides of the general formula I, ##STR1## where R 1 , R 2 , R 3  and R 4  are independently hydrogen, C 1-C   4  -alkyl or C 1  -C 4  -alkoxy, by hydrogenating phthalic anhydrides of the general formula II, ##STR2## where R 1 , R 2 , R 3  and R 4  are each as defined above, with hydrogen in the presence of suspended catalysts of the Raney type in a hydrogenation apparatus by using a mixing apparatus to mix a liquid phase, which includes the catalyst and the phthalic anhydride used and resulting phthalide, and a gas phase, which includes the hydrogenating hydrogen, comprises using the mixing apparatus to introduce a mixing intensity of at least 50 W/l into the liquid phase.

This application claims priority under 35 U.S.C. 371 from PCT/EP97/05186filed Sep. 22, 1997.

DESCRIPTION

The present invention relates to a process for preparing phthalides bycatalytic hydrogenation of phthalic anhydrides with the aid of suspendedRaney catalysts.

DE-C-28 03 319 discloses preparing phthalide by catalytic hydrogenationof phthalic anhydride in the gas phase using copper and aluminumcatalysts. However, this process is prohibitively costly in the productisolation stage, involving as it does multistage condensation and adownstream waste gas scrub.

U.S. Pat. No. 4,485,246 discloses preparing phthalide from phthalicanhydride by hydrogenation using homogeneous ruthenium catalysts.Catalyst recovery is difficult in these processes.

EP-A-542 037 discloses a process for preparing phthalides by catalytichydrogenation of phthalic anhydride over fixed bed catalysts in tubularreactors or tube bundle reactors or suspended catalysts in a stirredautoclave. If batch operated, said process requires large amounts ofcatalyst and long hydrogenation times. Continuous operation requireshigh pressures to obtain complete conversion.

EP-B-89 417 describes the catalytic hydrogenation of phthalic anhydrideto phthalide with the aid of a nickel catalyst immobilized on a supportmaterial using autoclaves with lift stirrer and methyl benzoate asmandatory solvent. The process has the disadvantage of high catalystrequirements and long reaction times.

Houben/Weyl, Methoden der organischen Chemie, 6/2 (1963), pages 732 to733, and also U.S. Pat. No. 2,114,696 describe the hydrogenation ofphthalic anhydride to phthalide with the aid of Raney nickel catalyst ina shaking autoclave, but a hydrogen pressure of 165 bar and ethanol assolvent affords a phthalide yield of only 73%.

It is an object of the present invention to remedy the aforementioneddisadvantages of existing processes for the catalytic hydrogenation ofphthalic anhydrides.

We have found that this object is achieved by a novel and improvedprocess for preparing phthalides of the general formula I, ##STR3##where R¹, R², R³ and R⁴ are independently hydrogen, C₁ -C₄ -alkyl or C₁-C₄ -alkoxy, by hydrogenating phthalic anhydrides of the general formulaII, ##STR4## where R¹, R², R³ and R⁴ are each as defined above, withhydrogen in the presence of suspended catalysts of the Raney type in ahydrogenation apparatus by using a mixing apparatus to mix a liquidphase, which includes the catalyst and the phthalic anhydride used andresulting phthalide, and a gas phase, which includes the hydrogenatinghydrogen, which comprises using the mixing apparatus to introduce amixing intensity of at least 50 W/l into the liquid phase.

The process of the present invention makes it possible to perform thehydrogenation of phthalic anhydrides to the phthalides at low levels ofcatalyst, with a good space-time yield and in high selectivity.

Compared with the conventional processes for hydrogenating phthalicanhydride to phthalide with the aid of suspended Raney nickel, theprocess of this invention makes it possible to reduce the amount ofRaney catalysts used appreciably for the same hydrogenation time, or toshorten the hydrogenation time dramatically for a comparable amount ofRaney catalysts used.

The process of this invention surprisingly does not give rise to anydeactivation of the Raney catalysts as arises with the conventionalprocesses employing the customary mixing intensities in stirred orshaking autoclaves and which leads to long reaction times andcorrespondingly low space-time yields in such apparatus. In addition,the caking of the Raney catalysts which occurs in the conventionalprocesses and which makes it difficult to remove the Raney catalystsafter the reaction does not take place in the process of this invention.

As we have further found, the deactivation of the Raney catalysts whichoccurs in the conventional processes is likely to be attributable to theacidic by-products formed during the hydrogenation of phthalic anhydrideto phthalide, such as toluic acid and phthalic acid (formed fromunconverted phthalic anhydride and water of reaction), which combinewith the Raney metals to form sparingly soluble salts which in turn arepreferentially deposited on the catalyst surface. The introduction inthe process of this invention of very high mixing intensities of atleast 50 W/l gives rise to high shearing forces which are responsiblefor the continual removal of surface coatings of sparingly soluble metalsalts such as nickel salts from the suspended Raney catalyst particles,so that the catalyst surface remains active throughout the entirereaction (cf. P.H.M.R. Cramers et al, Process Intensification with BussLoop Reactors, in Proceedings of the Conference "Catalysis in MultiphaseReactors", Lyons, Dec. 7-9, 1994).

It is an essential feature of the process of this invention that themixing apparatus which, in the hydrogenation, both mixes the gas andliquid phases and maintains the catalysts in suspended form introducesparticularly high mixing intensities into the liquid phase, viz. atleast 50 W/l of liquid phase, preferably from 50 to 2000 W/l of liquidphase, especially from 100 to 500 W/l of liquid phase.

This method of working gives rise to the above-recited advantages overthe conventional hydrogenation processes which employ typical mixingintensities from 0.1 to 10 W/l of liquid phase as available for examplefrom stirred reactors or shaking autoclaves.

The process of this invention can be carried out using any arrangementof hydrogenation apparatus which allows the introduction of at least 50W/l via appropriate mixing apparatus. The process of this invention isadvantageously carried out in a loop reactor in which a recirculatingpump recirculates the liquid phase out of the reactor and feeds it backat the top of the reactor. The liquid phase may be fed back in, forexample, by spraying it in finely divided form into the gaseous hydrogenatmosphere of the reactor, in which case the mixing intensity stipulatedby this invention may be transferred to the liquid phase not only in theregion of the recirculating pump but also in the region of the spraynozzle. The hydrogenation of this invention is carried out withparticular advantage in a loop reactor comprising a gas and liquidrecirculation system coupled via a multistream ejector mixing nozzle.For example, the process is advantageously carried out in a loop reactorplant having the following features:

1: reactor

2: recirculating pump

3: heat exchanger for liquid phase

4: multistream ejector mixing nozzle

5: recirculating line for liquid phase

6: feed line for hydrogen

7: discharge line for gas phase

8: feed and discharge line for liquid phase

9: optionally heated reactor wall

a) liquid phase

b) gas phase.

The loop reactor plant introduces suitably high mixing intensitiesespecially in the region of the recirculating pump 2, via which anintensity of up to about 100 W/l can be introduced into the recirculatedliquid phase, and in the region of the multistream ejector mixing nozzle4, via which an intensity of from 200 to 800 W/l, locally up to 10,000W/l, can be introduced.

The mixing intensity introduced using the mixing apparatus of thehydrogenation is conveniently determined in the manner described in Ind.Eng. Chem. Res. 1992, 31, 949-958.

The catalytic hydrogenation is generally carried out at temperaturesfrom 50 to 400° C., preferably from 100 to 250° C., especially from 140to 220° C., and at pressures from 1 to 400 bar, preferably from 5 to 300bar, especially from 5 to 200 bar, particularly advantageously from 30to 120 bar.

The hydrogenation catalysts used for the process of this invention areRaney catalysts. Suitable Raney catalyts are Raney nickel, Raney iron,Raney cobalt, Raney copper, preferably Raney nickel.

The Raney catalysts may be doped with suitable metals to increase theactivity. It may be advantageous, for example, to use Raney nickelcatalysts doped with metals of the 1st transition group of the periodictable, generally silver, copper, preferably copper", with metals of the6th transition group of the periodic table, generally chromium,molybdenum or tungsten, preferably molybdenum, and/or with metals of the7th group of the periodic table, generally manganese, rhenium,preferably rhenium. In general, the level of doping metals in the Raneynickel catalysts ranges from 0.01 to 10% by weight, preferably 0.1 to 5%by weight, based on the nickel present in the catalysts.

The Raney catalysts used according to this invention are prepared in aconventional manner. Raney nickel is obtained, for example, by alloyingnickel and alkali-leachable substances, preferably aluminum and/orsilicon, and subsequently leaching the alkali-soluble substances outusing an alkali, such as aqueous sodium hydroxide solution.

The hydrogenation can be carried out without solvent, in which case thephthalic anhydride is used in molten form.

In general, the hydrogenation is carried out using a solvent. Examplesof suitable solvents are ethers such as tetrahydrofuran, dioxane, glycolethers, esters such as methyl acetate and methyl benzoate, lactones suchas butyrolactone or phthalide, preferably the phthalide formed in thecourse of the hydrogenation, alcohols such as methanol, ethanol,propanol, butanol, hydrocarbons or mixtures thereof.

The weight ratio of phthalic anhydride to be hydrogenated to the solventused is generally within the range from 1000:1 to 1:1000, preferablywithin the range from 500:1 to 1:500, especially within the range from200:1 to 1:200.

The reaction of this invention is advantageously discontinued as soon asall the phthalic anhydride used has been hydrogenated. The time fordiscontinuation is determined for example by determining the phthalicanhydride still present, for example by gas chromatography or from thetime course of hydrogen consumption.

The reaction product is worked up in a conventional manner, preferablyby distillation.

In the compounds I and II, R¹, R², R³ and R⁴ are independently hydrogen;C₁ -C₄ -alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, sec-butyl, tert-butyl, preferably methyl and is ethyl,especially methyl; C₁ -C₄ -alkoxy such as methoxy, ethoxy, n-propoxy,isopropoxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, preferablymethoxy and ethoxy, especially methoxy. R¹, R², R³ and R⁴ areparticularly preferably all hydrogen.

The phthalic anhydrides II used as starting materials are well known,such as phthalic anhydride itself, or are obtainable by known processes(J. of Org. Chemistry 51, 3439-3446 (1986); Synthesis 223-224 (1985)).

The phthalides I are useful for example as starting materials for thesynthesis of crop protection agents.

The Examples which follow illustrate the invention.

INVENTIVE EXAMPLE 1

A 70 l loop reactor is charged with 39.5 kg of phthalide as solvent,16.9 kg of phthalic anhydride (PA) and 169 g Raney nickel (B 113 W fromDegussa), which is suspended in butyrolactone, at 130° C. in the form ofa melt. The reactor contents are recirculated at 5 m³ /h. The mixingintensity introduced into the liquid phase is 100 W/l in the region ofthe recirculating pump and 1000 W/l in the region of the multistreamejector mixing nozzle. Hydrogen is injected to a pressure of 40 bar andthe reactor contents are heated to 170° C. over 20 min. Thehydrogenation is carried out 40 bar and 170° C. to constant pressure.Hydrogen uptake is 5700 standard 1. The hydrogenation time is 102 min.

The product obtained is a colorless melt of the composition pressure.Hydrogen uptake is 5700 standard 1. The hydrogenation time is 102 min.

The product obtained is a colorless melt of the composition

Phthalide 94.1% by weight

Water 4.0% by weight

PA 0.3% by weight

Toluic acid 1.4% by weight.

This corresponds to a PA conversion of 99% coupled with a selectivity of93%.

COMPARATIVE EXAMPLE 2

A 0.5 l stirred autoclave equipped with a sparging stirrer is chargedwith 88.8 g of phthalic anhydride (PA), 207.2 g of phthalide and 0.90 gof Raney nickel (B 113 W from Degussa) in the form of a melt at about120° C. After the stirrer has been switched on, hydrogen is injected toa pressure of 40 bar and the reactor contents are heated to 180° C. Thehydrogenation is continued at this pressure and this temperature toconstant pressure, while the contents are stirred at a speed of 500 or1000 rpm. The experimental conditions and the results of thehydrogenation are summarized in the following table:

    ______________________________________                                                       Hydrogena-               Hydrogen                                 Speed tion time Conversion Selectivity uptake                                Run No. rpm min % % standard 1                                              ______________________________________                                        2a     500     235       99.9    85     25.1                                    2b 1000 225 99.7 83 24.8                                                    ______________________________________                                    

Composition of products in % by weight

    ______________________________________                                        Run No.   Phthalide                                                                              Water     PA   Toluic acid                                 ______________________________________                                        2a        92.3     3.3       <0.1 3.2                                           2b 91.9 3.4 0.1 3.7                                                         ______________________________________                                    

The present comparative example requires significantly longerhydrogenation times than Inventive Example 1 to achieve, what is more,distinctly lower selectivities.

INVENTIVE EXAMPLE

    __________________________________________________________________________    Concentration of PA                                                             based on PA +  Catalyst quantity Hydrogen Hydrogenation                     Run                                                                              phthalide   % by weight,                                                                        uptake                                                                             time   Conversion                                                                          Selectivity                              No. % by weight g based on PA standard 1 min % %                            __________________________________________________________________________    3a 30        43                                                                              0.25.sup.1)                                                                         5800 160     99   88                                       3b 30  54 0.35.sup.2) 5200 144  99 88.5                                       3c 50 210 0.75.sup.2) 9700  65 100 88.6                                     __________________________________________________________________________     .sup.1) butyrolactonemoist                                                    .sup.2) watermoist                                                       

COMPARATIVE EXAMPLE 4

A 2 l autoclave equipped with a lift stirrer is charged with 413 g ofphthalic anhydride (PA), 964 g of phthalide (688.5 g of PA and 688.5 gof phthalide for 4c) and the amount of Raney nickel reported in thetable, as a melt. After inertizing with nitrogen and replacing withhydrogen, the reactor contents are heated to the reported temperature ata lift count of 160 per minute and the reported hydrogen pressure isinjected. Hydrogenation is continued under these conditions to constantpressure.

The experimental conditions and the results are summarized in thefollowing table:

    __________________________________________________________________________                 Catalyst quantity                                                                      Hydrogen                                                                           Hydrogenation                                      Run                                                                              Temperature                                                                         Pressure                                                                             % by weight,                                                                        uptake                                                                             time   Conversion                                                                          Selectivity                             No. °C. bar g based on PA standard 1 min % %                         __________________________________________________________________________    4a 170   40  4.13                                                                             1.0.sup.1)                                                                          136  365    100   75                                      4b 183 80 1.03 0.25.sup.1) 137 1162  100 79                                   4c 183 80 1.45 0.35.sup.1) 137 435 100 85                                     4d 183 80 5.16 0.75.sup.2) 208 164  99 87                                   __________________________________________________________________________     .sup.1) butyrolactonemoist                                                    .sup.2) watermoist                                                       

The present comparative example requires signficantly longerhydrogenation times than Inventive Example 3.

We claim:
 1. A process for preparing phthalides of the general formulaI, ##STR5## where R¹, R², R³ and R⁴ are independently hydrogen, C₁ -C₄-alkyl or C₁ -C₄ -alkoxy, by hydrogenating phthalic anhydrides of thegeneral formula II, ##STR6## where R¹, R², R³ and R⁴ are each as definedabove, with hydrogen in the presence of suspended catalysts of the Raneytype in a hydrogenation apparatus by using a mixing apparatus to mix aliquid phase, which includes the catalyst and the phthalic anhydrideused and resulting phthalide, and a gas phase, which includes thehydrogenating hydrogen, which comprises using the mixing apparatus tointroduce a mixing intensity of at least 50 W/l into the liquid phase.2. The process of claim 1, wherein the mixing intensity introduced iswithin the range from 50 to 10,000 W/l.
 3. The process of claim 1,wherein the hydrogenation is carried out in a loop reactor comprising agas and liquid recirculation system coupled via a multistream ejectormixing nozzle.
 4. The process of claim 1, wherein the Raney catalystsare Raney nickel, Raney cobalt or Raney copper.
 5. The process of claim4, wherein the Raney catalyst is Raney nickel.